The field of the invention relates to generating swirl and/or tumble in a mixture inducted into the combustion chamber of an internal combustion engine.
It is desirable to increase the rotational movement of a mixture inducted into an internal combustion engine for increasing the burn rate thereby improving combustion efficiency. This phenomenon has been used to enable an increase exhaust gas recirculation and thereby achieve a reduction in emissions of nitrogen oxides. For gasoline engines, the inducted mixture is air/fuel and recirculated gas. In the case of diesel engines, the inducted mixture is air and recirculated gas. In either case, the strategy is to optimize angular momentum flux of the inducted mixture such that turbulence, and therefore mixing, continues after the intake valve is closed.
Angular momentum may be increased by generating a swirl pattern of the inducted mixture wherein the rotational velocity field has a center axis in line with the bore axis of the combustion chamber. Tumble may also be used to increase angular momentum by generating a tumble pattern of the inducted mixture wherein the rotational velocity field has a center axis normal to the bore axis of the combustion chamber.
A common approach for increasing swirl of the inducted measure is to extend a mask from the cylinder head partially surrounding the intake valve. During the portion of the valve intake stroke wherein the valve does not clear the mask, the inducted mixture is partially blocked by the mask such that the mixture is directed into a swirl pattern. During the portion of the intake valve stroke in which the valve seat clears the mask, inducted flow is far less restricted resulting in substantially less swirl.
A problem with conventional approaches of masking the intake valve is that neither swirl nor the volume of inducted flow per unit of time are maximized. That is, substantial swirl is only generated during the portion of the intake stroke in which the valve seat remains below the mask. And, inducted flow is only optimized, to the extent permitted by the mask, when the valve seat clears the mask. Even during maximum valve lift, inducted flow suffers some restriction from the mask.
U.S. Pat. No. 4,285,310 issued to Takizawa et al addresses only one of the two problems discussed above. More specifically, the Takizawa et al patent addresses the problem of a limitation on maximum inducted flow resulting from a mask or similar restriction. The Takizawa et al patent does not appear to address the problem of less than optimal swirl being generated. More specifically, the Takizawa et al patent provides both a primary and secondary intake valve. The primary valve appears to be conventional and is partially surrounded by a shroud for producing swirl. The secondary valve, which is a variable lift valve, lacks the shroud for producing a swirl. The secondary valve remains closed during light load conditions and opens only during heavy engine load conditions for increasing inducted flow. Allegedly, during heavy load conditions, inducted flow is optimized by action of the secondary valve. A disadvantage of this approach is that swirl does not appear to be optimized. Stated another way, during light load conditions, substantial swirl appears to be generated only during the portion of the valve stroke in which the primary valve remains below the mask. Another disadvantage is the added complexity of auxiliary valve and associated driving mechanisms.